// 2、无头双向链表实现
public class LinkedList {
    class ListNode{
        int val;
        ListNode prev;
        ListNode next;
        public ListNode(int val) {
            this.val = val;
        }
    }

    public ListNode head;
    public ListNode last;
    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if(head == null){
            head = last =  node;
            return;
        }

        node.next = head;
        head.prev = node;
        head = node;
    }
    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(head == null){
            head = last =  node;
            return;
        }

        last.next = node;
        node.prev = last;
        last = node;

    }
    //任意位置插入,第一个数据节点为0号下标
    public void addIndex(int index,int data){
        if(!checkIndex(index)){
             throw new IndexException("下标不合法");
        }

        if(index == 0){
            addFirst(data);
        }

        if(index == size()){
            addLast(data);
        }

        ListNode node = new ListNode(data);
        ListNode cur = head;
        for(int i = 0; i < index; i++){
            cur = cur.next;
        }
        ListNode curPrev = cur.prev;
        curPrev.next = node;
        node.prev = curPrev;
        node.next = cur;
        cur.prev = node;

    }

    private boolean checkIndex(int index){
        if(index < 0 || index > size())
            return false;
        return true;
    }
    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        ListNode cur = head;
        while(cur != null){
          if(cur.val == key){
              return true;
          }
        }
        return false;
    }
    //删除第一次出现关键字为key的节点
    public void remove(int key){
        ListNode cur = head;
        while(cur != null){
            if(cur.val == key){
                break;
            }
            cur = cur.next;
        }

        if(cur == head){
            head = head.next;
            head.prev = null;
        }

        if(cur == last){
            last = last.prev;
            last.next = null;
        }

        ListNode curPrev = cur.prev;
        ListNode curNext = cur.next;
        curPrev.next = curNext;
        curNext.prev = curPrev;

    }
    //删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur = head;
        while(cur != null){
            if(cur.val == key){
                if(cur == head){
                    head = head.next;
                    head.prev = null;
                } else if(cur == last){
                    last = last.prev;
                    last.next = null;
                } else{
                    ListNode curPrev = cur.prev;
                    ListNode curNext = cur.next;
                    curPrev.next = curNext;
                    curNext.prev = curPrev;
                }
            }

            cur = cur.next;
        }

    }
    //得到单链表的长度
    public int size(){
        ListNode cur = head;
        int count = 0;
        while(cur != null){
            count++;
            cur = cur.next;
        }
        return count;
    }

    public void display(){
        ListNode cur = head;
        while(cur != null){
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        System.out.println();
    }

    public void clear(){
        ListNode cur = head;
        while(cur != null){
            ListNode curNext = cur.next;
            cur.next = null;
            cur.prev = null;
            cur = curNext;
        }

        head = null;
        last = null;
    }


    public static void main(String[] args) {
        LinkedList list = new LinkedList();
//        list.addFirst(1);
//        list.addFirst(2);
//        list.addFirst(3);
//        list.addFirst(4);
//        list.display();

        list.addLast(1);
        list.addLast(2);
        list.addLast(2);
        list.addLast(3);
        list.addLast(3);
        list.addLast(4);
        list.display();
        list.removeAllKey(4);
        list.display();
    }

}